A cellular communication system includes a base station and at least one mobile device. The base station and the mobile device communicate using a radio-frequency (RF) link. Specifically, the base station transmits RF signals to the mobile device through a downlink, and the mobile device receives those RF signals. Conversely, the mobile device transmits RF signals to the base station, and the base station receives those signals via an uplink.
The base station in a conventional cellular system typically employs multiple antennas. Using the multiple antennas, the base station can use a technique called beam-forming. Beam-forming allows the base station to transmit a spatially directional RF signal to the mobile device.